1. Field of the Invention
This invention relates to an elect ostatic focusing and deflection system for use with electron beams, and especially with electron beams in cathode-ray tubes.
2. Description of the Prior Art
It is well known that a uniform longitudinal magnetic field, generated for instance by a long solenoid, focuses an electron beam. It is also well known that transverse magnetic fields, as generated by either saddle-shaped coils or toroidal coils, deflect an electron beam. Furthermore, a combination of both types of fields, as used in certain types of vidicons, can focus and deflect an electron beam simultaneously, along an axial region of a beam device where both the solenoid and deflection coils are located. The necessary independence of focusing and deflection action is achievable for magnetic fields because of the small coupling that exists between the focusing and deflection coils.
Simultaneous electrostatic focusing and deflecting cannot be achieved, using conventional electrode structures as focusing electrostatic lenses or deflection fields, such as cylinders and apertured disks of lenses and parallel or bent plates of deflecting systems. The electrode structures necessary for creation of one field will tend to mask any additional field which one attempts to superimpose upon the first field.
In U.S. Pat. No. 2,312,723 to Llewellyn, there was disclosed a composite cylindrical electrode having different potentials imposed upon different parts of the electrode in order to produce a parallel accelerating field. No selective deflection was provided by this electrode.
U.S. Pat. No. 2,453,647 to Van Overbeek teaches the use of a zigzag-shaped line of demarcation to divide two adjacent electrostatic deflecting members.
U.S. Pat. No. 3,397,341 teaches the use of a conical electrostatic deflector comprising four deflection electrode segments, each segment including a cutout into which is extended a protrusion from an annular conducting portion at one end of the electrode segments.
U.S. Pat. Nos. 3,678,316 and 3,678,320 to Barten teach the use of grid in a cathode-ray tube having boundaries between them in a sinusoidal shape.
It has, however, remained a problem to superimpose two electrostatic fields for simultaneous electrostatic focusing and deflection of a single electron beam.